1. Field of Invention
The present invention relates to technical fields of electro-optical devices and electronic apparatuses, and in particular to, technical fields of an electro-optical device including storage capacitors for improving potential-maintaining characteristics of pixel electrodes, and an electronic apparatus including the electro-optical device. Also, the present invention relates to technical fields of electrophoresis devices, such as electronic paper, EL (electroluminescent) devices, devices using electron emission elements (Field Emission Display and Surface-Conduction Electron-Emitter Display), etc.
2. Description of Related Art
An electro-optical device is known which includes pixel electrodes arranged in a matrix, thin film transistors (hereinafter referred to as xe2x80x9cTFTsxe2x80x9d,) respectively connected to the electrodes, and scanning lines and data lines which are provided in parallel to row and column directions, whereby so-called active-matrix driving can be performed. This electro-optical device further includes a TFT array substrate on which the above pixel electrodes, the TFTs, etc., are formed, an opposing substrate on which a common electrode opposed to the array substrate is formed, and electro-optical material, such as liquid crystal provided between both substrates, whereby a picture can be displayed. Specifically, in active matrix driving, each predetermined picture signal is written in the predetermined pixel electrode, whereby an electric field corresponding to the picture signal is applied and changes the state of each pixel, thus changing the transmission factor of light. For example, see Patent Document 1.
In this case, for example, when the scanning lines are provided, a predetermined time is required, from a state in which TFTs connected to one scanning line are switched on to a state in which the TFTs are next switched on, until selection of all the scanning lines is completed. In addition, since a voltage applied to the pixel electrodes and the electro-optical material, such as liquid crystal, is attenuated in the predetermined time, the picture is affected, although the state is unchanged.
Accordingly, an electro-optical device of the related art may include a storage capacitor on the TFT array substrate, in addition to the above components. This is a capacitor which includes a pair of substrates having a dielectric film provided therebetween and in which, simultaneously with the application of picture signals to pixel electrodes and the application of a predetermined electric field to electro-optical material, such as liquid crystal, an equal electric field is applied to the capacitor. By utilizing this storage capacitor, during the selection period for all the scanning lines, as described above, typically, in, for example, one field, the electric field to the electrical material, such as liquid crystal can be maintained as it was originally applied. Thus, a high quality picture can be displayed.
Nevertheless, the electro-optical device of the related art has a problem in that the storage capacitance cannot be set sufficiently large. When the storage capacitance cannot be set sufficiently large, maintenance of the electric field applied to the electro-optical material, such as liquid crystal cannot sufficiently be performed during the all selection period, thus causing display non-uniformity, flickering, etc., in a picture.
Although there are demands to increase the storage capacitance in order to cope with the above problem, it is difficult to satisfy these demands as size reduction, increased resolution, or increased aperture ratio of the electro-optical device advances. By way of example, to simply realize an increase in storage capacitance, it is possible to attempt to increase the areas of upper and lower electrodes, etc., constituting the storage capacitor. However, in this case, it is impossible for the electro-optical device to cope with the fundamental demand to display a bright picture since a decrease in the aperture ratio is inevitable.
In addition, although, to achieve increased storage capacitance, it is possible to reduce the distance between the upper electrode and the lower electrode, that is, to make a dielectric film thin, such attempts have already reached their limit since, even in the present circumstances, large reductions in the thickness of the dielectric film have already been made.
The present invention is made to address the above problems, and provides an electro-optical device in which a high quality picture free from display non-uniformity, flickering, etc., can be displayed, with increased storage capacitance while maintaining a high aperture ratio, and an electronic apparatus including the electro-optical device.
To address the above problem, a first electro-optical device of an aspect of the present invention includes data lines extending in a first direction above a substrate, scanning lines which extend in a second direction and which cross the data lines, pixel electrodes and thin film transistors disposed so as to correspond to regions in which the data lines and the scanning lines cross, storage capacitors electrically connected to the thin film transistors and the pixel electrodes, and a shield layer disposed between the data lines and the pixel electrodes. An upper electrode and a lower electrode between which a dielectric film forming each storage capacitor is supported include a first portion laminated along a plane parallel with one surface of the substrate and a second portion laminated along a plane orthogonal to the surface of the substrate, whereby the sectional shape of the capacitor includes a projecting shape.
According to the first electro-optical device of an aspect of the present invention, firstly, scanning lines, data lines, pixel electrodes, and thin film transistors are provided, whereby active-matrix driving can be performed. Also, in the above electro-optical device, each of the above components of various types forms part of a laminated structure, whereby size reduction of the entire device can be achieved, and appropriate disposition of the components is realized, whereby a pixel aperture rate can be increased. Also, provision of a shield layer between each data line and each pixel electrode can reduce or prevent capacitive coupling from occurring between both. In other words, power supply to the data lines can reduce a possibility that a potential change in the pixel electrode, etc., occur, thus enabling display of a high quality picture. In addition, in an aspect of the present invention, a storage capacitor is provided which is formed by an upper electrode and a lower electrode between which a dielectric film is provided, and in which one of the upper electrode and the lower electrode is connected to the pixel electrode. Accordingly, when an electric field corresponding to the picture signal is applied to the pixel electrode, the same electric field is stored in the storage capacitor. Therefore, an electric field applied to liquid crystal can be maintained in a predetermined period. Thus, according to an aspect of the present invention, a high quality picture free from flickering, etc., can be displayed.
Here, in particular, in an aspect of the present invention, the storage capacitor includes a first portion laminated along a plane parallel to one surface of the substrate, with the dielectric film provided between the upper electrode and the lower electrode, and a second portion laminated along a plane orthogonal to the surface of the substrate, whereby the sectional shape of the capacitor includes a projecting shape. In other words, for example, in accordance with a case, such as the formation of the lower electrode so that it includes a projecting portion from the substrate, or the formation of a projecting member in a predetermined position below the lower electrode, the dielectric film and the upper electrode which are positioned above has a bending shape in a sectional view. In this case, compared with a plane storage capacitor of the related art, an operation and advantage of an increase in capacitance is expected for only the area of the second portion which is laminated along a plane orthogonal to the surface of the substrate, and in which the upper electrode, the dielectric film, and the lower electrode are laminated, that is, the area of a side wall having a projecting shape.
Accordingly, in an aspect of the present invention, the capacitance of the storage capacitor can be increased without increasing the two-dimensional areas of the upper electrode and the lower electrode constituting the storage capacitor. Thus, an increase in the storage capacitance is realized, whereby a high quality picture free from display non-uniformity, flickering, etc., can be displayed.
Moreover, in the present invention, the dielectric film constituting each storage capacitor may include a plurality of layers including different materials, and may constitute a laminated body including one of the layers which includes a material having a dielectric constant higher than those of the other layers. Thus, the charge-storage characteristics of the storage capacitor can be more enhanced.
Also, this point greatly contributes to high quality picture display in the electro-optical device of an aspect of the present invention.
A form in which the sectional shape of the storage capacitor includes the projecting shape is realized, as described above, by the formation of the lower electrode so as to include a projecting portion, and the formation of a projecting member below the lower electrode. However, in an aspect of the present invention, the form may be realized using any suitable device or method. For example, in a case in which some wires and circuit elements, etc., are formed below the lower electrode, and an interlayer insulating film is formed on them, when the surface of the interlayer insulating film has a difference in level in accordance with the height of each of the wires and circuit elements, etc., it is possible that the difference in level be used as a base for the second portion or the projecting shape. In other words, in this case, by sequentially forming the lower electrode, the dielectric film, and the upper electrode, on the difference in level, a storage capacitor whose sectional shape naturally includes a projecting shape can be formed.
Depending on the circumstance, a form maybe employed in which a depression is formed in the interlayer insulating film on the substrate, the lower electrode and the dielectric film are formed to cover the depression. The upper electrode is formed so as to fill in the depression and to cover the surface of the interlayer insulating film.
Moreover, in an aspect of the present invention, one of the upper electrode or the lower electrode, which constitute the storage capacitor, is connected to the pixel electrode, thereby having a potential equal to that in the pixel electrode. In this case, it is preferable that the other electrode, which is not connected to the pixel electrode, has a fixed potential. In this case, the upper electrode or the lower electrode, which is connected to the pixel electrode, can be generally called the xe2x80x9cpixel-potential capacitor electrodexe2x80x9d, and the other electrode can be called the xe2x80x9cfixed-potential capacitor electrodexe2x80x9d. Here, an electrode connected to the pixel electrode may be either an upper or lower electrode. Thus, regarding the more actual configuration of the storage capacitor, a laminated structure may be employed which is composed of the pixel-potential capacitor electrode, the dielectric film, and the fixed-potential capacitor electrode on the substrate in sequential order from the bottom, or the structure having a reverse order may be employed.
In connection with the above, the above fixed-potential capacitor electrode may be formed as part of a capacitor line formed along the direction in which the scanning lines extend. This enables the time or cost required for production to be reduced. This is because, although the formation of separately forming fixed-potential capacitor electrodes to be separate or isolated on the substrate requires provision of wires for each electrode, by forming each fixed-potential capacitor electrode as part of the capacitor xe2x80x9clinexe2x80x9d since the fixed-potential capacitor electrode only needs to have a fixed potential, one wire may be provided for the capacitor line, and a production cost can be correspondingly reduced.
In addition, as material for the above upper electrode and lower electrode, basically, any material may be selected. Preferably, for example, one of the upper electrode and the lower electrode may be formed of a light shielding material. This enables the upper electrode or the lower electrode to undertake the role of a light shielding layer for preventing light from being incident on the channel region of each thin film transistor. Thus, the generation of a light leakage current in the channel region is suppressed, whereby a high quality picture can be displayed in which flickering, etc., caused by the current, do not occur.
Moreover, the xe2x80x9chigh dielectric constant materialxe2x80x9d in the present invention includes insulating material or the like which includes, not only silicon nitride, which is described later, but also at least one of the group including TaOx (tantalum oxide), BST (strontium barium titanate), PZT (zirconate titanate), TiO2 (titanium oxide), ZiO2 (zirconium oxide), HfO2 (hafnium oxide), SiON (silicon oxynitride), and SiN (silicon nitride). In particular, by using high dielectric constant materials of TaOx, BST, PZT, TiO2, ZiO2 and HfO2, capacitance in a limited region on the substrate can be increased. Alternatively, by using silicon-included materials of SiO2 (silicon oxide), SiON (silicon oxynitride), and SiN, the generation of a stress in the interlayer insulating film or the like can be reduced.
To address the above problem, a second electro-optical device of an aspect of the present invention includes data lines extending in a first direction above a substrate, scanning lines which extend in a second direction and which cross the data lines, pixel electrodes and thin film transistors disposed so as to correspond to regions in which the data lines and the scanning lines cross, storage capacitors electrically connected to the thin film transistors and the pixel electrodes, and a light shielding film disposed between each data line and each pixel electrode. An upper electrode and a lower electrode, between which a dielectric film forming each storage capacitor is supported, include a first portion laminated along a plane parallel with one surface of the substrate and a second portion laminated along a plane orthogonal to the surface of the substrate, whereby the sectional shape of the capacitor includes a projecting shape.
According to a second aspect of an electro-optical device of the invention, a light shielding film is provided instead of the shield layer in the above first electro-optical device. Therefore, the presence of the light shielding film increases the light shielding feature of the thin film transistor, whereby the generation of a light leakage current, the generation of flickering caused by the current, etc., can be reduced.
Also, by forming the storage capacitor so as to be confined in a light shielding region defined by the light shielding film, the aperture ratio can be maintained at a high level.
According to this aspect, the sectional shape of the storage capacitor includes a projecting shape despite the maintenance of the high aperture ratio, whereby the capacitance can be increased.
A form may be employed in which the light shielding film and the above shield layer in the present invention coexist, or in which a member having the functions of both, that is, a light-shielding-film-and-shield-layer is provided.
In an aspect of the first electro-optical device of the present invention, the shield layer is electrically connected to the upper electrode of the storage capacitor.
According to this aspect, the shield layer and the upper electrode of the storage capacitor have equal potentials. More specifically, both can be maintained so as to have the same fixed potential. According to this, by connecting either one to a power supply to supply a fixed potential, the other one can simultaneously have the fixed potential. Thus, simplification, etc., of a device configuration are realized. Also, the laminated structure can be optimized.
In another aspect of the first electro-optical device and an aspect of the second electro-optical device in the present invention, the projecting shape is formed, such that the lower electrode is formed so as to include a projecting portion from the substrate.
According to this aspect, the lower electrode itself is formed so as to include the projecting portion, whereby a storage capacitor according to the present invention which includes a projecting shape can be relatively easily formed. In other words, in this case, the formation of the lower electrode in a form integrated with the projecting portion in a lower electrode forming process so as to include the projecting portion, that is, the formation of the projecting portion as the same film for the lower electrode, can be performed. Thus, a production step can be simplified.
More specifically, the formation of the lower electrode including the projecting shape can be performed by after an original film to become the lower electrode in the future is formed, a resist film is formed on only a portion to be left as a projecting shape in the original film, and etching thereon is implemented.
In another aspect of the first or second electro-optical device of the present invention, the projecting shape is formed by forming a projecting member below the lower electrode.
According to this aspect, as described above, the lower electrode is not formed so as to include the projecting portion, but, a projecting member separated therefrom is formed below the lower electrode, whereby the projecting shape is formed. Therefore, this case may have a form in which the material for the lower electrode and the material for the projecting member are set to differ.
Also, in another aspect of the first or second electro-optical device of the present invention, the lower electrode may be formed of a light absorbing conductive material.
According to this aspect, the lower electrode, which is a thick film, can increase a light absorbing effect.
In another aspect of the first or second electro-optical device of the present invention, the projecting shape includes a tapered shape.
According to this aspect, good formation of the dielectric film and the upper electrode to be formed on the lower electrode can be performed. In other words, when the projecting shape includes the tapered shape, one corner of the projecting shape is smoothed, as is clear from comparison with, for example, a projecting shape having a perpendicular side wall. Thus, in the formation of the dielectric film and the upper electrode on the projecting shape including the tapered shape, there is almost no need of concern about deterioration in coverage, etc. Therefore, according to this aspect, good formation of the dielectric film and the upper electrode can be performed.
Also, in the case of comparison between a projecting shape including a perpendicular side wall and the projecting shape according to this aspect, which includes the tapered shape, when it is assumed that the heights of both are equal and the areas of the top surfaces of the projecting shapes are equal, in general, the area of the side wall is larger in the latter than in the former. Thus, the latter is preferable in a storage capacitance increasing point.
In another aspect of the first or second electro-optical device of the present invention, the height of the projecting shape is 50 to 1000 nm.
According to this aspect, the capacitance of the dielectric film can be increased at least approximately 1.5 times a reference value of a plane storage capacitor of the related art, although it differs depending on various conditions, such as a point in which what material is used to form the dielectric film. Therefore, according to this aspect, for the increase, a potential holding characteristic can be enhanced, thus enabling reduction in the generations of display non-uniformity, flickering, etc., in a picture.
According to another aspect of the electro-optical device of the present invention, the pixel electrodes are arranged in a matrix, the scanning lines and the data lines are formed in light shielding regions corresponding to the matrix, and the storage capacitors are formed in the light shielding regions.
According to this aspect, the formation of the storage capacitors in the light shielding regions can maintain the aperture ratio so as to have a high value. In addition, according to this aspect, the capacitance of the each storage capacitor can be increased, since its sectional shape, includes a projecting shape despite the maintenance of the high aperture ratio.
Therefore, according to this aspect, a bright picture can be displayed, and a high quality picture free from display non-uniformity, flickering, etc., can be displayed.
Each light shielding region is a region in which light contributing to picture display is shielded, and its specific shape differs depending on what shape the above xe2x80x9cmatrixxe2x80x9d has. For example, when the matrix represents a case in which the pixel electrodes are linearly arranged in vertical and horizontal directions, the specific shape of the light shielding regions is a lattice. Aside from this, when the pixel electrodes are arranged in a hound""s-tooth-check form in vertical and horizontal directions, the specific shape of the light shielding regions is a shape such, as one in which curved lines bending along edges of the pixel electrodes are arranged in parallel in vertical and horizontal directions.
In another aspect of the first or second electro-optical device of the present invention, the projecting shape of the storage capacitor is formed along at least one of each scanning line and each data line.
According to this aspect, lamination of the interlayer insulating film, etc., on the projecting shape forms a projecting portion on the projecting shape. Thus, a form in which the projecting portion extends along one of the scanning line and the data line appears. Therefore, in this case, a form in which the projecting portion exists between adjacent pixel electrodes appears. Accordingly, in the case of using a 1H inversion driving method, a 1S inversion driving method, or a dot inversion driving method to drive the electro-optical device according to this aspect, an adverse effect on the picture, which is caused by a lateral electric field generated between adjacent pixel electrodes, can be reduced, thus enabling display of a high quality picture. The reason is described below in detail.
In the 1H inversion driving method, for example, when pixel electrodes arranged in a square form are assumed, a state in which, in one frame or field, pixel electrodes arranged in odd-numbered rows thereof are driven by a positive polarity potential, with the potential of a common electrode used as a reference, and pixel electrodes arranged in even-numbered rows are driven by a negative polarity potential, and a state in which, in the subsequent frame or field, conversely, driving is performed so that the negative polarity potential is used for the odd-numbered rows and the positive polarity potential is used for the even-numbered rows, are repeated. Also, the 1S inversion driving method is a driving method that can be understood in a form in which, in the description of the 1H inversion driving method, the odd-numbered rows are replaced by xe2x80x9codd-numbered columnsxe2x80x9d, and the even-numbered rows are replaced by xe2x80x9ceven-numbered columnsxe2x80x9d. In addition, in the dot inversion driving method, the polarity of a voltage applied to each pixel electrode is inverted between adjacent pixel electrodes in column and row directions. By employing these driving method, deterioration in electro-optical material, such as liquid crystal, which is caused by the application of a direct-current voltage component, or the generation of crosstalk or flickering in the picture can be suppressed.
However, a so-called xe2x80x9clateral electric fieldxe2x80x9d is generated because, in each inversion driving method, pixel electrodes to which voltages having different polarities are applied are adjacent to one another. For example, in the 1H inversion driving method, between pixel electrodes positioned in one row, and pixel electrodes positioned in a row adjacent thereto, a lateral electric field is generated. The generation of the lateral electric field creates disorder in the potential difference (hereinafter referred to as the xe2x80x9clongitudinal electric fieldxe2x80x9d) between each pixel electrode on the substrate and the common electrode on the opposing substrate, and causes inferior alignment in liquid crystal, so that insufficient light intensity in the corresponding portion occurs, resulting in a deterioration in picture quality, such as a decrease in picture quality.
Accordingly, in this aspect, as described above, the projecting shape of the storage capacitor is formed along one of the scanning line and the data line, whereby the lateral electric field can be reduced or prevented from being generated.
This is because, by forming each pixel electrode so that its edge is on an edge of the projecting portion, the distance between the pixel electrode and the common electrode can be narrowed, whereby the longitudinal electric field can be enhanced compared with the above-described case. Also, this is because the lateral electric field can be weakened, depending on the magnitude of the dielectric constant of the projecting portion, regardless of whether or not the edge of the pixel electrode exists on the projecting portion. In addition, this is because the influence of the lateral electric field on liquid crystal can be relatively reduced since the volume of the gap between the projecting portion and the common electrode, that is, the volume of the liquid crystal in the gap, can be reduced.
Needless to say, in the 1H inversion driving method, it is preferable that the projecting shape or the projecting portion be formed along the scanning line, and in the 1S inversion driving method, it is preferable that the projecting shape or the projecting portion be formed along the data line. Also, in the dot inversion driving method, the projecting shape or the projecting portion be formed along both the scanning line and the data line.
As described above, according to this aspect, good application of the longitudinal electric field to the liquid crystal can be performed, whereby a picture as desired can be displayed.
In another aspect of the first or second electro-optical device of the present invention, the dielectric film includes a silicon oxide film and a silicon nitride film.
According to this aspect, the dielectric film includes a silicon nitride film having a relatively high dielectric constant. Thus, a high charge storage characteristic can be enjoyed, even if the area of the storage capacitor, that is, the area of a pair of electrodes constituting the storage capacitor, is slightly reduced.
This greatly enhances the potential holding characteristic of the pixel electrode, thus enabling display of a high quality picture. Also, the area of the storage capacitor can be further reduced in a plane view, thus enabling a further increase in the aperture ratio.
In addition, since the silicon nitride film has a good operation of stemming infiltration or diffusion of moisture, it can reduce or prevent moisture from infiltrating into the semiconductor layer forming the thin film transistor. In this respect, if moisture infiltrates into the semiconductor layer, the gate insulating film, or the like, positive charge is generated in the interface between the semiconductor layer and the gate insulating layer, thus resulting in an adverse effect in that a threshold voltage gradually increases. In this aspect, as described above, infiltration of moisture into the semiconductor layer can be effectively reduced or prevented, thus enabling reduction or prevention of an occurrence of a problem in that the threshold voltage gradually increases.
In addition, the dielectric film includes a silicon oxide film in addition to the above silicon nitride film, whereby the breakdown characteristic of the storage capacitor does not decrease.
As described above, according to the dielectric film according to this aspect, multiple operations and advantages can be simultaneously enjoyed.
This aspect includes, not only a case in which the dielectric film has a two-layered structure composed of a silicon oxide film and a silicon nitride film, but also, depending on the circumstance, a case in which the dielectric film has a three-layered structure composed of, for example, a silicon oxide film, a silicon nitride film, and a silicon oxide film, or a case in which the dielectric film has a laminated structure composed of more than three layers.
In another aspect of the electro-optical device of the present invention, an interlayer insulating film, disposed as a base for each pixel electrode, is further provided as a part of the laminated structure, and one surface of the interlayer insulating film is subjected to planarization processing.
According to this aspect, a possibility of creating disorder in the alignment state of electro-optical material, such as liquid crystal, can be reduced, whereby a high quality picture can be displayed.
An electronic apparatus of an aspect of the present invention includes the above-described electro-optical device of the present invention. However, it includes each aspect of the device.
The electronic apparatus of an aspect of the present invention includes the above-described electro-optical device of the present invention, that is, an electro-optical device in which storage capacitance is increased while maintaining a high aperture ratio. Thus, a bright picture can be displayed, and various electronic apparatuses that can display a high quality picture free from display non-uniformity, flickering, etc., such as projection display devices, liquid crystal television, cellular phones, electronic books, word processors, view-finder or direct-monitor-view videotape recorders, workstations, videophones, POS terminals, and touch panels can be realized.
The above operations and other advantages of the present invention become apparent from exemplary embodiments described below.